Re: [PATCH 0/1] __asm_copy_to-from_user: Reduce more byte_copy

From: Qiu Wenbo <qiuwenbo@kylinos.com.cn>
To: Akira Tsukamoto <akira.tsukamoto@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Guenter Roeck <linux@roeck-us.net>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/1] __asm_copy_to-from_user: Reduce more byte_copy
Date: Sun, 15 Aug 2021 10:30:06 +0800	[thread overview]
Message-ID: <21b55fd7-7ab5-10e9-4fc9-1815ec95927d@kylinos.com.cn> (raw)
In-Reply-To: <a70451d1-57ad-6b49-24c1-6408ef94a959@gmail.com>

Hi Akira,

This patch breaks my userspace  and I can't boot my system after 
applying this. Here is the stack trace:

[   10.349080] Unable to handle kernel NULL pointer dereference at 
virtual address 0000000000000000
[   10.357116] Oops [#15]
[   10.359433] CPU: 2 PID: 169 Comm: (networkd) Tainted: G D           
5.14.0-rc5 #53
[   10.367422] Hardware name: SiFive HiFive Unmatched A00 (DT)
[   10.372981] epc : __asm_copy_from_user+0x48/0xf0
[   10.377584]  ra : _copy_from_user+0x28/0x68
[   10.381754] epc : ffffffff8099a280 ra : ffffffff803614a8 sp : 
ffffffd00416bd90
[   10.388963]  gp : ffffffff811ee540 tp : ffffffe0841b3680 t0 : 
ffffffd00416bde0
[   10.396172]  t1 : ffffffd00416bdd8 t2 : 0000003ff09ca3a0 s0 : 
ffffffd00416bdc0
[   10.403381]  s1 : 0000000000000000 a0 : ffffffd00416bdd8 a1 : 
0000000000000000
[   10.410590]  a2 : 0000000000000010 a3 : 0000000000000040 a4 : 
ffffffd00416be18
[   10.417800]  a5 : 0000003ffffffff0 a6 : 000000000000000f a7 : 
ffffffe085d58540
[   10.425009]  s2 : 0000000000000010 s3 : ffffffd00416bdd8 s4 : 
0000000000000002
[   10.432218]  s5 : 0000000000000000 s6 : 0000000000000000 s7 : 
ffffffe0841b3680
[   10.439427]  s8 : 0000002aad788040 s9 : 0000000000000000 s10: 
0000000000000001
[   10.446636]  s11: 0000000000000000 t3 : 0000000000000000 t4 : 
0000000000000001
[   10.453845]  t5 : 0000000000000010 t6 : 0000000000040000
[   10.459144] status: 0000000200040120 badaddr: 0000000000000000 cause: 
000000000000000d
[   10.467049] [<ffffffff8099a280>] __asm_copy_from_user+0x48/0xf0
[   10.472955] [<ffffffff8009a562>] do_seccomp+0x62/0x8be
[   10.478079] [<ffffffff8009af58>] prctl_set_seccomp+0x24/0x32
[   10.483725] [<ffffffff80020756>] sys_prctl+0xf6/0x450
[   10.488763] [<ffffffff800034f2>] ret_from_syscall+0x0/0x2

The PC register points to this line:

+1:
+	REG_L	a5, 0(a1)

Qiu

On 8/12/21 7:01 PM, Akira Tsukamoto wrote:
> Hi Guenter, Geert and Qiu,
>
> Would you mind testing this patch?
> Thanks,
>
> Akira
>
> On 7/30/2021 10:50 PM, Akira Tsukamoto wrote:
>> Adding none unrolling word_copy, which is used if the size is smaller
>> than 9*SZREG.
>>
>> This patch is based on Palmer's past comment.
>>> My guess is that some workloads will want some smaller unrolling factors,
>> It will reduce the number of slow byte_copy being used when the
>> size is small.
>>
>> Have tested on qemu rv32, qemu rv64 and beaglev beta board.
>>
>> In the future, I am planning to convert uaccess.S to inline assembly
>> in .c file. Then it will be easier to optimize on both in-order core and
>> out-of-order core with #ifdef macro in c.
>>
>> Akira Tsukamoto (1):
>>    riscv: __asm_copy_to-from_user: Improve using word copy if size <
>>      9*SZREG
>>
>>   arch/riscv/lib/uaccess.S | 46 ++++++++++++++++++++++++++++++++++++----
>>   1 file changed, 42 insertions(+), 4 deletions(-)
>>

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